What Would Drupal Do?

No, you're absolutely right.

Really on the module level this is already accomplished via nodeapi -- the upload module for example adding the 'Attachments' dialog, which is like attributes on steroids.

I guess what I'm thinking of is something at a higher level for those using Drupal as a CMS, rather than those coding for Drupal. So that "registered attributes" (the terminology needs to be clearer, granted) would be as straightforward to manage and assign as terms in a taxonomy. The underlying mechanism would certainly be handled primarily via nodeapi, but should be transparent to the user.

Essentially the functionality of nodeapi brought into the backend admin interface for use by those who aren't interested or don't have the skills to add code to a custom module. Presently, those who are just trying to assemble a website with Drupal tend to rely on methods like the ones I described above -- they aren't writing custom code that makes use of the apis, they are finding workarounds through the tools available to them in the admin section and theme hacks. There are good reasons why they do this -- they aren't developers, and aren't interested in Drupal internals.

You're completely right, I just suspect that we are thinking of different types of users.

It also provides incentive for those of us who are coding modules to build consensus around certain terms so that our modules can act on those in predictable ways. (The "votable" or "allows_voting" example)